The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
With the increasing cost associated with energy as well as the increased environmental concerns associated with fuel, there is an increasing demand to develop solutions that can decrease energy demands. Heating and cooling costs are the highest component of energy cost. In a typical household heating and cooling cost are about 45% to the total energy cost. With fuel cost rising and increased environmental awareness, there is a need to improvise ways to reduce energy consumption and to reduce emission of greenhouse gases.
During winter months, windows and other fenestrations typically account for highest heat loss through them and the outside temperature, Tout, is typically cooler than the desired comfortable temperature inside the building, i.e., Tdesired>Tout. In order to maintain the comfortable temperature inside the building some sort of heating device is used which raises the temperature in the interior of the building to Tinside and maintains it at this level by replacing the heat lost through the windows or similar openings. The heat loss is governed by the laws of physics and thermodynamics that dictate that the heat flows from higher temperature, Tinside to lower temperature, Tout. If this lost heat is not replaced, the temperature inside will start to fall and will eventually become equal to the colder temperature, Tout. Thus in order to maintain a comfortable temperature, Tinside>Tout, the continuous use of a heating device is necessary (see FIG. 1).
FIG. 1 shows a cross-sectional view of a window 104 installed in a building. The window 104 separates the outside 101 from the interior 100 of the building. The window 104 held in place by a window frame 103 that is installed in a wall 102. A furnace or other heating device 105 attempts to maintain the interior temperature of the building at a desired interior temperature Tinside.
For a given size window 103, the amount of heat loss per unit area of the window generally depends on two parameters; a U-factor and the difference between the inside and outside temperatures, Tinside−Tout. Generally, heat loss can be characterized as:{dot over (q)}=−k(Tinside−Tout)  (1)
where:
{dot over (q)} is the heat loss per unit time; and
k=the thermal conductance.
The temperature difference (Tinside−Tout) is the driving force behind the heat loss (transfer). If k=0, then the material is called a perfect insulator and {dot over (q)}=0. However, the conductance, k can be very small but not equal to zero. As equation (1) shows, for a given temperature difference, the smaller k is, the smaller the heat loss. To understand the function of an insulator, consider FIG. 2.
In FIG. 2, L represents the thickness of the insulator 200 and A represents the area covered by the insulator (for example it can be the area of a window). The temperature T1 is the warmer side and k is the conductance of the insulating material.
For this case equation (1) is rewritten as,
                    k        =                              q            .                                -                          (                                                T                  1                                -                                  T                  2                                            )                                                          (        2        )            
From equation (2) it is seen that as long as there is a temperature difference, when k=0, {dot over (q)}=0. Furthermore when k is small, {dot over (q)} is also small. Equation (2) can also be expressed as:
                    κ        =                              q            .                                              -                              (                                                      T                    1                                    -                                      T                    2                                                  )                                      ⁢                          A              /              L                                                          (        3        )            
The constant, κ is called the thermal conductivity and 1/κ is called the thermal resistivity, and is defined as:
                              1          κ                =                                            (                                                T                  2                                -                                  T                  1                                            )                        ⁢            A                                              q              .                        ⁢            L                                              (        4        )            
The quantity κ/L is called the U-factor of the insulator, the inverse of which is called the R-value. The R-value is a measure of a building material's thermal resistance typically used in industry. Insulators with a small U-factor (high R-value) reduce the heat transfer. As the definition of the U-factor suggests that in order to have a small U-factor, the insulator must have greater thickness, L, or smaller conductance (poor conductor of heat), κ or both. Equation (4) suggests that the smaller the U-factor (larger R-value) the smaller the heat flow across A. Thus, use of insulators having a high R-value reduces the heat transfer resulting in less heat lost to the outside when the interior of the building is heated and less heat gained from outside when the same is cooled.
Most contemporary buildings in the United States have double pane, or so-called insulated windows and often these windows are tinted to control the amount of radiant heat transmitted through the window. Two pane tinted windows have the so-called R-value of approximately 2. This low R-value causes substantial heat transfer across the window panes. If somehow the heat transfer across the windows can be mitigated, the net result would be a substantial reduction in energy usage either when the building is cooled during the summer months or when the building is heated during the winter months. It should be appreciated that “window” is used for all possible openings including doors, such as the patio glass doors and the like.
When an insulator is not present, as shown in FIG. 1, the heat loss, {dot over (q)}loss to the outside in the winter months will be greater compared to the case when an insulator 300 is present as shown in FIG. 3. The window insulator 300 coupled to the window 104 reduces the U-factor of the opening thus reducing the heat transfer (loss) to the outside in winter months. Thus, when the window insulator is present, more heat is retained in the interior. The burning time of the furnace will be less. Hence the use of a window insulator results in cost savings and less green-house gases will be released into the atmosphere.
In the summer months, when Tout is greater than Tinside, the heat transfer takes place from outside into the interior of the living space. The influx of heat raises the temperature of the living space. The heat flow continues until Tout=Tinside. To cool the interior of the building, heat should be removed from the interior. This is customarily accomplished by an air-conditioning unit 106 (FIG. 4). The window insulator 300 in summer months reduces the heat entering from the outside to inside due to conduction. However, the window insulator 300 fails to prevent heat gain due to thermal radiation. Radiative heat transfer is more prevalent during the summer when the temperature outside, Tout is greater than the temperature inside, Tinside. Generally, window insulators do not address this issue. Therefore, the temperature inside the building can still be significantly increased due to radiation heat gain from the sun even when these insulators are in place.
Use of curtain hanging devices are typically employed with the aforementioned insulators. Often these devices conflict with the existing mounting devices or fixtures. Furthermore, additional fixtures or mounting device may not be aesthetically pleasing. Accordingly, there is a need for an insulating window screen that can be mounted on the window without any devices or fixture, which will result in a space saving footprint and little or no cost and labor associated with such equipment.